Interaction of vitamin D receptor and androgen receptor in human prostate cancer cell line

Abstract

9550 Background:Calcitriol has significant antitumor activity in vitro and in vivo in human prostate cancer as well as many other tumor types. Calcitriol and analogs modulate cell cycle proteins, including p27 and p21 and apoptosis, as assessed by cleavage of caspase 3, PARP and MEK. Calcitirol has antitumor effects which appear to be different in androgen dependent and androgen independent tumor cells However, the mechanisms by which calcitriol and the vitamin D receptor (VDR) interact with the androgen receptor (AR) signaling pathway is not known. The purpose of the study is to investigate the l interaction of VDR and AR in prostate cancer. We sought to evaluate VDR-AR “cross-talk”. Method: LNCaP cells, a human prostate cancer cell line were grown in phenol red free media, supplemented by 5% charcoal stripped serum. Western blot analyses were performed to analyze the protein level. Results: We demonstrated that when the cells were treated with calcitriol (10 nM), the AR protein level increased as soon as 4 hours after treatment by Western blot analysis. The AR protein level was further enhanced if both calcitriol (10 nM) and dihydroxytestosterone (10 nM) were added compared to either agent alone. To examine AR protein stability, we added cycloheximde (25 μg/ml), which inhibits the cellular protein synthesis, during the 4-hour treatment of calcitriol or DHT and calcitriol. We demonstrated by Western blot analysis that calcitriol increases the stability of the AR protein and calcitriol plus DHT can further increase the stability at four hours while DHT did not significantly change AR protein level. Although the AR protein level was increased with calcitriol treatment, the DHT-induced hyperphosphorylation of pRB was blocked by calcitriol as shown by the Western blot analysis. This suggests that cell proliferation is inhibited by calcitriol + DHT rather than being stimulated. Conclusions:Based on our results, we postulate that VDR and AR interact either directly or indirectly at the receptor level in human prostate cancer cell and suggests there may be a role for treatment approaches targeting both receptor axes. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novocea Pharmaceuticals